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Vibrational spectra and assignment, ab initio calculations and normal coordinate analysis for 3 methyl 3 vinyl cyclopropene

The Raman spectra (3400–10 cm−1) of liquid and solid 3-methyl-3-vinylcyclopropene, C3H2(CH3)CHCH2, and its isotopomer C3D2(CH3)CHCH2 were recorded. The temperature dependence of some band intensities and qualitiative depolarization ratios show that the thermodynamically preferred conformation is s-trans. The structural parameters and conformational stability of s-trans and gauche rotamers were obtained from ab initio calculations by employing both 3–21G and 6–31G* basis sets. Barriers to internal rotation and fundamental vibrational frequencies were calculated utilizing the 3–21G basis set. The ab initio results are consistent with the experimentally indicated greater stability of the s-trans relative to the gauche conformer.

vibrational spectra ; 3-methyl-3-vinylcyclopropene

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